The present invention is directed generally to fiber optic devices, and more particularly to a method and apparatus for aligning a fiber optic device that includes collimator sub-assemblies.
Optical fibers find many uses for directing beams of light between two points. Optical fibers have been developed to have low loss, low dispersion, polarization maintaining properties and can also act as amplifiers. As a result, optical fiber systems find widespread use, for example in optical communication applications.
However, one of the important advantages of fiber optic beam transport, that of enclosing the optical beam to guide it between terminal points, is also a limitation. There are several optical components, important for use in fiber systems or in fiber system development, that are not implemented in a fiber-based form where the optical beam is guided in a waveguide. Instead, these optical components are implemented in a bulk form and through which the light propagates freely. Examples of such components include, but are not limited to, filters, isolators, circulators, polarizers, switches and shutters. Consequently, the inclusion of a bulk component in an optical fiber system necessitates that the optical fiber system have a section where the beam path propagates freely in space, rather than being guided within a fiber.
Free space propagation typically requires use of collimation units, also known as collimator sub-assemblies, at the ends of the fibers to produce collimated beams. Therefore, a device may have a collimator sub-assembly at each end, defining one or more collimated beam paths to their respective fibers. Light from an input fiber is collimated by the first collimator unit and passes through free space to the second collimator unit, where it is focused into an output fiber. One difficulty in manufacturing a fiber optic device is ensuring that the collimated beam paths from the two collimator sub-assemblies are collinear.
Mechanically, many of the prior art approaches to aligning collimator sub-assemblies are less than elegant. Typically, the two sub-assemblies are adjusted in space by tooling until good optical coupling is achieved. They are then immersed in a xe2x80x9csea of gluexe2x80x9d to fix their positions. (The xe2x80x9csea of gluexe2x80x9d fills the space between the outside of the sub-assembly and the inside of the module housing.) There are typically no mechanical supports for the sub-assemblies except for the glue itself. One of the drawbacks to the xe2x80x9csea of gluexe2x80x9d is that the thermal expansions of the glue and the housing may be different, and so any asymmetry in the glue distribution may produce some shifting of the components as the temperature changes. Also the glue lines are thick, uneven, and vary from assembly to assembly. This leads to complex and, therefore, often labor intensive, procedures for aligning modules that include sub-assemblies.
Generally, the present invention relates to a module where two sub-assemblies are fitted to respective end faces of a central section. The end faces of the central section are non-parallel, and permit the adjustment of the two sub-assemblies in substantially decoupled degrees of freedom.
One particular embodiment of the invention is directed to a fiber optic device having a longitudinal axis. The device includes a first sub-housing disposed on the longitudinal axis and has first and second end faces. The first end face defines a first plane parallel to a first transverse axis perpendicular to the longitudinal axis, where the first plane is non-parallel to i) the longitudinal axis and ii) a second transverse axis that is perpendicular to both the longitudinal axis and the first transverse axis. The second end face defines a second plane parallel to the second transverse axis, where the second plane is non-parallel to i) the longitudinal axis and ii) the first transverse axis. The device also includes a second sub-housing disposed on the longitudinal axis and has a third end face parallel to the first end face. The third end face is fitted to the first end face. The device also includes a third sub-housing disposed on the longitudinal axis. The fourth sub-housing has a fourth end face fitted to the second end face of the first sub-housing.
Another embodiment of the invention is directed to a method of aligning a fiber device. The method includes providing a first sub-housing on a longitudinal axis. The first sub-housing has first and second end faces, where the first end face defines a first plane parallel to a first transverse axis perpendicular to the longitudinal axis. The first plane is non-parallel to i) the longitudinal axis and ii) a second transverse axis perpendicular to both the longitudinal axis and the first transverse axis. The second end face defines a second plane parallel to the second transverse axis. The second plane is non-parallel to i) the longitudinal axis and ii) the first transverse axis. The method also includes fitting a third end face of a second sub-housing to the first end face of the first sub-housing and fitting a fourth end face of a third sub-housing to the second end face of the first sub-housing. The method further includes adjusting position of the second sub-housing with the third end face fitted to the first end face and adjusting position of the third sub-housing with the fourth end face fitted to the second end face.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.